The study of the free swimming of undulating bodies in an otherwise quiescent fluid has always encountered serious difficulties for several reasons. When considering the full system, given by the body and the unbounded surrounding fluid, the absence of external forces leads to a subtle interaction problem dominated, at least at steady state conditions, by the equilibrium of strictly related internal forces, e.g. thrust and drag, under the forcing of a prescribed deformation. A major complication has been dictated by the recoil motion induced by the non linear interactions, which may find a quite natural solution when considering as unknowns the velocity components of the body center of mass. A simplified two-dimensional model in terms of impulse equations has been used and a fruitful separation of the main contributions due to added mass and to vorticity release is easily obtained. As main results we obtain either the mean locomotion speed and the oscillating recoil velocity components which have a large effect on the overall performance of free swimming. Several constrained gaits are considered to highlight the relevance of recoil for realizing graceful and efficient trajectories and to analyze its potential means for active control.

出于多种原因，对波状体在其他方式静止的流体中自由游动的研究一直遇到严重的困难。当考虑由人体和不受限制的周围流体给定的整个系统时，缺少外力会导致一个细微的相互作用问题，至少在稳态条件下，该问题主要由严格相关的内力（例如推力和阻力）的平衡所决定，在规定的变形的作用下。非线性相互作用引起的后坐运动决定了主要的并发症，当将质心的速度分量考虑为未知数时，这可能会找到很自然的解决方案。使用了一个基于脉冲方程的简化二维模型，由于增加了质量和释放了涡度，很容易就可以将主要贡献进行有效的分离。作为主要结果，我们获得了平均运动速度和摆动后坐速度分量，这些分量对自由泳的整体性能影响很大。考虑了几种约束步态，以突出后坐力对实现优美有效轨迹的重要性，并分析其主动控制的潜在手段。